1. Field of the Invention
The present invention relates to: an optical information recording medium which utilizes both groove regions (i.e., guide grooves) and land regions (i.e., regions between grooves) as information tracks, the grooves and lands having been previously formed on the optical information recording medium; and an optical information recording/reproduction device for recording an information signal on the optical information recording medium.
2. Description of the Related Art
In recent years, there have been vigorous research and development activities for realizing optical information recording media for recording and reproducing information signals (e.g., video signals and audio signals) thereon. One example of such an optical information recording medium is an optical disk. A recordable optical disk includes guide grooves (hereinafter referred to as "grooves") previously engraved on a substrate, the grooves constituting information tracks. Any region between adjoining grooves is referred to as a "land". Information signals can be recorded or reproduced on the optical disk by converging a laser light beam on the flat portions of grooves or lands.
In the case of common commercially-available optical disks, information signals are typically recorded on either grooves or lands. When information signals are recorded on the grooves, for example, the lands serve as guard bands for separating adjoining tracks defined by the grooves. In the case where information signals are recorded on the lands, the grooves serve as guard bands.
FIG. 9 is a magnified perspective view of a conventional optical disk having the above-mentioned structure. In FIG. 9, reference numeral 85 denotes a recording layer (which may be composed of a phase-change material, for example); 86 denotes a recording pit; 87 denotes a laser beam spot; 88, 90, and 92 denote guide grooves defining "grooves"; 89 and 91 denote "lands"; 93 denotes a transparent substrate through which light enters. As seen from FIG. 9, grooves are made wider than lands in this exemplary conventional optical disk.
In an attempt to increase the recording capacity of the above conventional optical disk, the interspaces between tracks are shortened by narrowing the widths of the lands 89. However, a smaller interspace between tracks results in a larger diffraction angle of light reflected from the grooves. This results in a lower level of tracking error signal, which is employed to ensure accurate tracing of the beam spot 87 on the tracks.
Moreover, there is a limit to the increase in track density achieved by merely reducing land widths. However, reducing the groove widths might lower the amplitude of the reproduced signal due to thinner recording pits 86.
On the other hand, there are techniques for increasing the track density, such as that disclosed in Japanese Patent Publication No. 63-57859, according to which information signals are recorded on both grooves and lands.
FIG. 10 is a magnified perspective view of such an optical disk. In FIG. 10, reference numeral 85 denotes a recording layer; 86 denotes a recording pit; 87 denotes a laser beam spot; 93 denotes a transparent substrate; 94, 96, and 98 denote grooves; 95 and 97 denote lands.
As shown in FIG. 10, the grooves and the lands have substantially the same width. Pre-pits 99, which are formed for both grooves and lands, are engraved at the beginnings of sectors of both information tracks (i.e., groove and lands) as identification signals representing locational information on the optical disk.
In the above optical disk, the recording pits 86 are formed for both groves and lands as shown in FIG. 10. Although the grooves have a period equal to the period of grooves in the optical disk shown in FIG. 9, each interspace between adjoining recording pit rows in FIG. 10 is half of that of the optical disk shown in FIG. 9. As a result, the optical disk in FIG. 10 has twice as large a recording capacity as that of the optical disk in FIG. 9.
Rewritable optical disks require identification signals (indicating location information on the disk), etc., to be previously recorded on the disk. The inventors of the present invention have proposed in Japanese Laid-Open Patent Publication No. 6-176404 a technique of recording one identification signal for an adjoining pair consisting of a groove and a land so as to be located between the groove and the land.
However, in the above-mentioned optical information recording media, the track pitch is reduced to half of that of conventional optical information recording media, thereby requiring an even more accurate track servo control. Particularly when an identification signal is recorded between a land and its corresponding groove, only one half of the beam spot will be incident on the pre-pits. Therefore, when the beam spot shifts away from the track center, toward regions where the identification signal is not present, it may be impossible to detect the identification signal.